Here are a few easy to do side trips when visiting Florence Italy.

Siena: It's an hour either by bus or train.  The bus from Florence takes you right into the center of historic Siena and the train probably requires a short taxi ride, but I prefer the train - the bus can be a bit hectic.  The Piazza del Campo slopes down and makes it a perfect place to sit and enjoy a gelato.  The never completed Duomo is a spectacular example of Renaissance razzle-dazzle. The Piccolomi library's frescoes are a joy.  It's easy to spend 3/4 of a day in Siena.

Pisa: Get from Florence to Pisa Centrale in about an hour by train. Take the bus or a taxi over to the Piazza dei Miracoli, walk past the souvenir stands and get a selfie with the Leaning Tower of Pisa.  The baptistry is worth a look too.  But after it's all said and done, it will take a half day or less to see all the sights.

Lucca:  This is The Traveling Professor's favorite side trip from Florence. What I would do is after visiting Pisa, hop on the bus or train for the short ride to Lucca.  Lucca, due to its heavy fortification, is probably one of the best preserved old cities.  The food cannot be beat.  The wall circling the city is wide enough to put a bike/walking path.  I like to rent a bike, ride atop the walls and peer inside the gardens of the well-appointed homes. It's always fun to climb to the top of Guinigi Tower, visit the beautiful botanical gardens, and check out the home of Puccini, a master of opera.  There always seems to be a market, a concert, or some other activity going on in Lucca.  Try it. You'll like it.

Join The Traveling Professor on a small group tour to Italy.